Methods and devices for regulating speed and/or acceleration are conventional under the term “tempomat”. Supplementing such a device with a sensor, which can recognize preceding vehicles and/or obstacles located in the direction of travel, is also known. These devices may utilize, in the control of vehicle speed, not only their own internal traffic variables, but also traffic variables of the surroundings. Such devices are denoted as adaptive or dynamic vehicle speed controllers or adaptive cruise control (ACC). Such an adaptive travel regulating system may be a convenient assistance to a driver. Therefore, the acceleration and deceleration dynamics, with which the control system activates the forward propulsion and the brakes of the vehicle, may be limited. Furthermore, the adaptive vehicle speed regulator neither should nor can relieve the driver of any responsibility. Instead, the regulator may only relieve the driver of monotonous and tiring activities. Therefore, existing ACC systems may be deliberately made incapable of independently initiating either sharp or full braking, even though the sensory system may be capable of recognizing dangerous situations. In these dangerous situations, existing ACC systems provide a so-called request for taking control,-which is activated when the maximum deceleration provided by the automatic system may be no longer sufficient to avoid a collision. The request for taking control signals the driver acoustically, optically, haptically or kinesthetically that manual intervention using the brake pedal may become necessary. In supplementary fashion, the driver has priority over the vehicle control system at all times, in that he may operate the gas or brake pedal and override or deactivate the system, thereby putting the automatic drive control out of commission.
A fundamental description of such a device is referred to in the paper “Adaptive Cruise Control—System Aspects and Development Trends,” given by Winner, Witte et al., at SAE 96, Feb. 26 to 29, 1996 in Detroit (SAE Paper No. 961010). The paper discusses the dynamic restriction of the system for the purpose of riding comfort.
The request for taking control is mentioned in this article as possibly being an acoustic signal which is activated when no sufficient deceleration can be made available so as to react fittingly to the instantaneous situation.
One method and device for travel regulation are described in German Published Patent Application No. 195 44 923. The system includes a radar system and a vehicle speed sensor, from the measured values of which, an acceleration requirement signal is formed. This signal is then used to activate the throttle and the brakes (EGAS system). A limiter assures that the acceleration requirement signal does not exceed the range between a predefined maximum or minimum value, in order to guarantee a designated travel comfort to vehicle passengers. In this system, the driver is notified by a blinking light, a tone generator, a haptic device or a combination of these possibilities. These signal elements are activated when the current deceleration requirement of the vehicle exceeds or approximately reaches the maximum permissible deceleration for the vehicle, and the vehicle is subject to travel control at the same time. European Published Patent No. 0 348 691 describes concepts for haptic signaling. However, no method is described which points to a reference for triggering a request for taking control.